Victron MPPT keeping my batteries at 80% even with bulk set to 100% — anyone else had this?

Had exactly this on the narrowboat last summer — drove me absolutely mad for about three weeks before I figured out what was going on.

Turned out my BatteryProtect and the MPPT weren't talking to each other properly over VE.Direct, and the controller was essentially taking its state-of-charge reference from a slightly dodgy shunt reading rather than actual voltage. The Cerbo GX was showing 100% on the dashboard whilst the batteries were sitting at a resting voltage that told a completely different story.

The fix for me was recalibrating the BMV-712 shunt — it had drifted after I'd done some work on the 12v circuits and hadn't properly zeroed it back out. Once that was sorted, the MPPT suddenly "knew" where it actually was in the charge cycle and bulk started behaving properly again.

A couple of things worth checking in your case:

• Tail current setting — if it's too high, the controller thinks absorption is complete earlier than it should
• Absorption time — is it set to fixed or adaptive? Adaptive can be sneaky
• Any load on the system during charging that might be confusing the current calculations

Also worth having a look in VictronConnect at the charge history graph. The shape of the bulk/absorption/float transitions will tell you a lot about what's actually happening versus what you think is happening.

What batteries are you running? Lithium or lead? Makes a big difference to how the MPPT interprets that 80% ceiling. If it's Fogstar or similar LiFePO4 with a BMS that's sending charge signals, that adds another layer to unpick.

@RiverSoul what were they talking over — VE.Direct or VE.Bus? Wondering if this is the same thing I'm experiencing on my static caravan setup.

Mine's a Victron SmartSolar 100/30 paired with Fogstar Drift lithium, and I've noticed it seems to plateau around 80% on cloudy days but I assumed that was just a solar availability issue rather than a comms problem. Now you've got me second-guessing myself.

Is there a way to diagnose whether the MPPT is receiving accurate SOC data, or does it basically just go off voltage? I'm using the Victron Connect app but I'm not sure I'm reading the right values. Would a Cerbo GX actually solve this or is that overkill for a caravan install?

@RiverSoul this is almost certainly a DVCC issue if you're running a Cerbo or Venus GX in the mix. When DVCC is enabled, the system CVL (charge voltage limit) gets handed down from the BMS via CAN-bus or VE.Direct, and it will override your MPPT's local absorption setting entirely — doesn't matter what you've programmed into VictronConnect.

Check your Cerbo under Settings → DVCC and look at what CVL is actually being broadcast. If your BMS is a Fogstar or similar that reports a conservative 80% SoC ceiling as its charge limit, that's exactly what the MPPT will honour.

@IvyWalker — VE.Direct vs VE.Bus matters less here than whether DVCC is active at all. VE.Bus devices get slightly different priority handling but the override behaviour is essentially the same.

@LazySocket is right about DVCC, but there's another culprit worth checking — shared current control within DVCC settings. Had mine set up on the Python last winter, Cerbo GX running the show, and the MPPT kept deferring to a CCL signal coming from the BMS rather than my absorption target.

Worth jumping into the Cerbo's DVCC menu and checking what's actually sending the charge current limit. On my setup it was the Fogstar Drift battery whispering "80% is fine, cheers" to the whole system via CANbus, completely overriding whatever the MPPT thought it was doing.

@IvyWalker — if you're on VE.Direct rather than VE.Bus, DVCC still applies if there's a GX device mediating everything. The physical cable doesn't matter once the Cerbo's orchestrating it all.

@TomCampbell raises a valid point on shared current control, but nobody's mentioned Battery Life yet.

If you've got Battery Life enabled on the MPPT (either directly or via the GX device overriding your settings), it deliberately limits SOC to around 80% as a protective measure when it decides the battery isn't being discharged deeply enough. It's trying to be clever and prevent surface charge issues on lead-acid.

Check in VictronConnect → your MPPT → Battery settings. If you see "Battery Life" active, disable it. On a narrowboat you're almost certainly cycling properly anyway, so it's just getting in the way.

Worth noting: if a GX device is connected and DVCC is on, the GX can re-enable Battery Life even after you've turned it off locally. You need to disable it from the GX settings, not just the MPPT directly.

@VictronMaster good shout on Battery Life — that caught me out proper on my boat. Worth adding though: check your absorption time settings too. If you're on a short solar day (trees, bridges, whatever) the MPPT might just be cutting absorption short and never fully topping off.

Also had a weird one where my temperature sensor was reading falsely high and the controller was compensating by dropping charge voltage. Worth ruling out if you've got one fitted.

Fogstar drift cells especially — they're pretty sensitive to voltage calibration being slightly off, so even a small discrepancy looks like it's stuck at 80%.